Update descriptor state allocation to match approach used in epoll_reactor.

diff --git a/asio/include/asio/detail/impl/kqueue_reactor.ipp b/asio/include/asio/detail/impl/kqueue_reactor.ipp
index d7b989c..3d0ccfd 100644
--- a/asio/include/asio/detail/impl/kqueue_reactor.ipp
+++ b/asio/include/asio/detail/impl/kqueue_reactor.ipp

@@ -125,9 +125,10 @@
 int kqueue_reactor::register_descriptor(socket_type descriptor,
     kqueue_reactor::per_descriptor_data& descriptor_data)
 {
-  mutex::scoped_lock lock(registered_descriptors_mutex_);
+  descriptor_data = allocate_descriptor_state();
 
-  descriptor_data = registered_descriptors_.alloc();
+  mutex::scoped_lock lock(descriptor_data->mutex_);
+
   descriptor_data->descriptor_ = descriptor;
   descriptor_data->shutdown_ = false;
 
@@ -142,9 +143,10 @@
     int op_type, socket_type descriptor,
     kqueue_reactor::per_descriptor_data& descriptor_data, reactor_op* op)
 {
-  mutex::scoped_lock lock(registered_descriptors_mutex_);
+  descriptor_data = allocate_descriptor_state();
 
-  descriptor_data = registered_descriptors_.alloc();
+  mutex::scoped_lock lock(descriptor_data->mutex_);
+
   descriptor_data->descriptor_ = descriptor;
   descriptor_data->shutdown_ = false;
   descriptor_data->op_queue_[op_type].push(op);
@@ -303,7 +305,6 @@
     return;
 
   mutex::scoped_lock descriptor_lock(descriptor_data->mutex_);
-  mutex::scoped_lock descriptors_lock(registered_descriptors_mutex_);
 
   if (!descriptor_data->shutdown_)
   {
@@ -338,11 +339,9 @@
 
     descriptor_lock.unlock();
 
-    registered_descriptors_.free(descriptor_data);
+    free_descriptor_state(descriptor_data);
     descriptor_data = 0;
 
-    descriptors_lock.unlock();
-
     io_service_.post_deferred_completions(ops);
   }
 }
@@ -354,7 +353,6 @@
     return;
 
   mutex::scoped_lock descriptor_lock(descriptor_data->mutex_);
-  mutex::scoped_lock descriptors_lock(registered_descriptors_mutex_);
 
   if (!descriptor_data->shutdown_)
   {
@@ -374,10 +372,8 @@
 
     descriptor_lock.unlock();
 
-    registered_descriptors_.free(descriptor_data);
+    free_descriptor_state(descriptor_data);
     descriptor_data = 0;
-
-    descriptors_lock.unlock();
   }
 }
 
@@ -510,6 +506,18 @@
   return fd;
 }
 
+kqueue_reactor::descriptor_state* kqueue_reactor::allocate_descriptor_state()
+{
+  mutex::scoped_lock descriptors_lock(registered_descriptors_mutex_);
+  return registered_descriptors_.alloc();
+}
+
+void kqueue_reactor::free_descriptor_state(kqueue_reactor::descriptor_state* s)
+{
+  mutex::scoped_lock descriptors_lock(registered_descriptors_mutex_);
+  registered_descriptors_.free(s);
+}
+
 void kqueue_reactor::do_add_timer_queue(timer_queue_base& queue)
 {
   mutex::scoped_lock lock(mutex_);

diff --git a/asio/include/asio/detail/kqueue_reactor.hpp b/asio/include/asio/detail/kqueue_reactor.hpp
index f1b220f..8a302f5 100644
--- a/asio/include/asio/detail/kqueue_reactor.hpp
+++ b/asio/include/asio/detail/kqueue_reactor.hpp

@@ -168,6 +168,12 @@
   // cannot be created.
   ASIO_DECL static int do_kqueue_create();
 
+  // Allocate a new descriptor state object.
+  ASIO_DECL descriptor_state* allocate_descriptor_state();
+
+  // Free an existing descriptor state object.
+  ASIO_DECL void free_descriptor_state(descriptor_state* s);
+
   // Helper function to add a new timer queue.
   ASIO_DECL void do_add_timer_queue(timer_queue_base& queue);